Yes, Buffy is always a slayer, regardless of what universe we are in. And Piper, Prue, Paige, and Phoebe are always witches, and the Hogwarts gang are always witches or wizards. It is just their magic is different in each one.

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Romeo take me somewhere we can be alone I'll be waiting all there's left to do is run
You'll be the prince and I'll be the princess. It's a love story, baby just say yes.